Right, that's my problem.
a drive is unplugged... while the system is not running mdadm will not reassemble the array on boot.
Red Hat Bugzilla – Bug 1451660 Write that Fixed In Version:dracut-033-546.el7
I have drucat version 033-554.el7 and this bag don't fixed!
I believe you are hitting this bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1451660
That is, if a drive is unplugged while the system is not running, mdadm will not reassemble the array on boot.
If a drive fails while the system is running, mdadm should fail it out of the array and the system will boot properly.
Hoping for a fix in the next minor release.